If $x \star y = 7x+y$ and $x \triangleleft y = 4x-y$, find $-3 \star (3 \triangleleft 6)$.
First, find $3 \triangleleft 6$ $ 3 \triangleleft 6 = (4)(3)-6$ $ \hphantom{3 \triangleleft 6} = 6$ Now, find $-3 \star 6$ $ -3 \star 6 = (7)(-3)+6$ $ \hphantom{-3 \star 6} = -15$.